Preparation method of aluminum alloy melt for die casting

Abstract

The invention relates to a preparation method of an aluminum alloy melt for die casting, which comprises the following steps: heating the aluminum alloy melt to 760-800 DEG C, transferring the aluminum alloy melt into a transfer ladle, introducing inert gas into a mixture of a refining agent and a fluxing medium at the rotating speed of 400-600r / min, and refining at 720-780 DEG C for 7-8 minutes; then, the rotating speed of the rotor is adjusted to 600-675 r / min, the flow of the inert gas is increased, the stirring speed is adjusted, refining is conducted for 10-15 min, and scum is blocked on one side through a scum blocking plate. And after refining is completed, slagging-off sampling is conducted on the melt, whether the gas content in the melt meets the standard of casting products or not is checked, and if yes, die casting is prepared. And all scum can be removed together, so that the production efficiency of the aluminum alloy die-casting process is remarkably improved.

Description

Technical Field

[0001] The invention relates to the field of aluminum alloy processing, and in particular to a method for preparing an aluminum alloy melt for die casting. Background Art

[0002] Aluminum and aluminum alloy materials are widely used in transportation, packaging containers, building decoration, aerospace, machinery and electrical appliances, electronic communications, petrochemical and other industries due to their low density, high specific strength, high specific stiffness, good elasticity, good impact resistance, corrosion resistance, wear resistance, high electrical conductivity, high thermal conductivity, easy surface coloring, easy processing, and recyclability. Especially in the die-casting industry, aluminum is the preferred lightweight structural material for parts in the communications industry and the automotive industry, and the amount of aluminum alloy die-casting is very large.

[0003] Some functional parts in automobiles and some other industries have the characteristics of high mobility, high load, high pressure resistance, high fatigue resistance, high speed and high reliability. Die-casting of these functional parts has very strict requirements on the quality of aluminum alloy smelting. Not only must the oxide layer and inclusion content in the aluminum alloy melt be strictly controlled, but the hydrogen content must be as low as possible. The refining process of aluminum alloy melt is also called the purification process of slag removal and degassing. The key is to remove hydrogen and oxide layer (Al2O3), non-metallic inclusions, other harmful metals and other impurities during the refining process to prevent the aluminum alloy material from loosening, forming pores and inclusions, so as to ensure the physical properties and other performance of the aluminum alloy. The quality of the refining process directly affects the quality of die-castings.

[0004] The current method of removing impurities and hydrogen from aluminum alloy melts is based on the bubble floatation theory, that is, blowing a large number of inert gas bubbles into the aluminum alloy melt, using a high-speed rotating rotor to break the bubbles into very small bubbles, and diffuse them throughout the molten metal. By reducing the bubble diameter, the surface of the inert gas is greatly increased, allowing more impurities and hydrogen to contact the bubble surface and separate from the aluminum liquid as the bubbles rise. From the perspective of microscopic theory, inclusions (impurities) with a diameter of 10 microns are adsorbed on the bubbles after contacting them, and hydrogen is absorbed into the bubbles and removed as the bubbles float to the liquid surface.

[0005] However, this method takes a long time to process and has low efficiency. For example, the impurity particle size in the aluminum alloy melt is uneven, and large impurities are not easily adsorbed by bubbles. It takes a long time for bubbles to be evenly distributed in the aluminum alloy melt. The longer the refining time, the aluminum alloy melt will continue to contact with oxygen to produce new aluminum oxide impurities. After the heat of the aluminum alloy melt is dissipated, the viscosity increases and the bubbles float more slowly, which will further reduce the degassing efficiency.

[0006] In addition to inert gas, another method is to add a refining agent containing chloride salt components to the aluminum alloy melt. The chloride salt reacts chemically with aluminum to produce aluminum chloride gas. These gases form bubbles that can carry the impurities and hydrogen dissolved in the aluminum alloy melt upward.

[0007] However, the refining agent tends to concentrate at the bottom center or surface of the melt and is difficult to be evenly dispersed in the aluminum alloy melt. The contact area between the refining agent and the melt is limited. Aluminum chloride bubbles only exist in the contact area between the refining agent and the melt. The impurities and hydrogen brought out are also limited to the contact part with the refining agent. The hydrogen and impurities in the local position of the aluminum alloy melt are difficult to contact with the aluminum chloride bubbles, and the effect of removing impurities and hydrogen is poor. The amount of refining agent added is difficult to control, impurities are easily introduced, and it is difficult to balance the impurity removal effect. Summary of the invention

[0008] The purpose of the present invention is to provide a method for preparing an aluminum alloy melt for die casting which is efficient and capable of removing large particle impurities in order to solve the problems existing in the existing refining process.

[0009] To achieve the above objectives, the present invention provides a method for preparing an aluminum alloy melt for die casting, comprising: Charge configuration step S1: According to the requirements of aluminum alloy products, aluminum alloy ingots and recycled materials are configured into charge in proportion. Melt preparation step S2: putting a charge into a graphite crucible furnace, heating and melting it, and removing the slag on the surface through a slag removal operation to obtain an aluminum alloy melt; Refining agent degassing step S3: pouring an aluminum alloy melt at a temperature of 760-800° C. from a graphite crucible furnace into a transfer bag, rotating the rotor at a speed of 400-600 rpm, introducing an inert gas into the aluminum alloy melt at a flow rate of 25-35 L / min and a gas pressure of 0.2 MPa, stirring the aluminum alloy melt into a vortex, adding a refining agent and / or a slag remover to the aluminum alloy melt in an amount of 1-2% of the weight of the melt, using the adsorption effect of the vortex to sink the refining agent and / or the slag remover to the bottom, and refining is performed at a temperature of 720-780° C. for 7-8 minutes; Inert gas degassing step S4: drop a slag baffle into the transfer bag to allow the slag baffle to penetrate into the aluminum alloy melt, adjust the rotor speed, the flow rate and pressure of the inert gas, adjust the rotor speed from 400-600 / min to 600-675 rpm, adjust the flow rate of the inert gas from 25-35 L / min to 2000-2500 L / min, and adjust the gas pressure from 0.2 Mpa to 0.3 Mpa, and continue refining for 10-25 minutes. Die casting preparation step S5: After slagging, the refined and degassed aluminum alloy melt is transferred from the transfer bag to a holding furnace, and the temperature of the aluminum alloy melt is adjusted to within the range required for die casting.

[0010] The preparation method of the present invention rationally utilizes the physical and chemical properties of the refining agent, slag removal agent and inert gas, can remove impurities and hydrogen of all particle sizes, effectively reduce the formation of pores, looseness, inclusions and other defects in the aluminum alloy die castings, and can ensure that the physical properties, mechanical properties and use performance of the aluminum alloy die castings are met. The process is simple and smooth, the program arrangement is reasonable, and the refining effect and production efficiency of the aluminum alloy die casting process can be significantly improved.

[0011] Preferably, the refining agent is manganese chloride or zinc chloride, and the slag-breaking agent is a mixture of sodium chloride, calcium chloride, cryolite, and sodium fluorosilicate, and the refining agent and the slag-breaking agent are mixed in a weight ratio of 1:1.5. After actual testing, the slag-breaking refining agent with the above components has the best effect.

[0012] Preferably, the charge includes fresh alloy aluminum ingots and recycled charge. In the melt preparation step S2, before the charge is put into the graphite crucible furnace, the charge is degreased, rusted, sanded, and inlaid. The charge also needs to be preheated to remove moisture from the surface of the charge, so as to prevent the wet charge from exploding due to a sudden temperature rise after entering the furnace. The charge is put into the graphite crucible furnace once or twice, the furnace temperature is set at 900±50℃, and the aluminum alloy melt is obtained by slagging when the temperature reaches 730℃, so as to prevent the increase of the content of oxide inclusions and gas in the melt.

[0013] Preferably, in the melt preparation step S2, the aluminum alloy melt is sampled after slag removal for spectral sample chemical composition detection. If the sample is unqualified, corresponding components of the charge should be added in time to adjust the sample so as to obtain the aluminum alloy melt for refining.

[0014] Preferably, in the refining agent degassing step S3 and the inert gas degassing step S4, the inert gas introduced is nitrogen or argon with a purity of 99.99%. After actual testing, the refining effect is best when nitrogen or argon with a purity of 99.99%.

[0015] Preferably, in the die-casting preparation step S5, after slag removal, sampling is performed to check whether the gas content in the aluminum alloy melt is qualified. If unqualified, the inert gas degassing step S4 is performed again. The staff can reasonably arrange the duration of the inert gas degassing step S4 according to the quality requirements of the die-casting products.

[0016] Preferably, the recycled materials include primary recycled materials, secondary recycled materials and tertiary recycled materials. The primary recycled materials refer to the clean castings that are not scrapped due to impurity content exceeding the standard, which can be directly used for batching without remelting, not exceeding 80% of the total weight of the recycled materials. The secondary recycled materials refer to the gates and handles of die castings, not exceeding 80% of the total weight of the recycled materials. The tertiary recycled materials refer to waste materials such as oily castings, slag bags, flash, etc., which need to be remelted and analyzed for composition before being used for batching, not exceeding 30% of the total weight of the recycled materials. Using recycled materials is to recycle the waste and waste materials generated in the refining process, which is beneficial to environmental protection and saving production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a flowchart illustrating a method for preparing an aluminum alloy melt for die casting; Figure 2 It is an analysis illustration diagram of a sample of AlSi12Fe melt that has not undergone the refining agent degassing step S3 and the inert gas degassing step S4 of Example 1; Figure 3 It is an analysis illustration diagram of a sample of AlSi12Fe melt that has undergone the refining agent degassing step S3 and has not undergone the inert gas degassing step S4 in Example 1; Figure 4 It is an analysis illustration diagram of sampling of the AlSi12Fe melt after the refining agent degassing step S3 and the inert gas degassing step S4 of Example 1; Figure 5 It is an analysis illustration diagram of the ADC12 melt sampling without the refining agent degassing step S3 and the inert gas degassing step S4 of Example 2; Figure 6 It is an analysis diagram of the ADC12 melt sampling after the refining agent degassing step S3 and without the inert gas degassing step S4 of Example 2; Figure 7 It is an analysis illustration diagram of ADC12 melt sampling after the refining agent degassing step S3 and the inert gas degassing step S4 of Example 2; Figure 8 is a schematic diagram of the state of the degassing refiner in the refining agent degassing step S3; Fig. 9 Schematic diagram of the state of the degassing refiner during the inert gas degassing step S4. DETAILED DESCRIPTION

[0018] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. The following description is a specific embodiment of the claims of the present invention.

[0019] In this embodiment, an aluminum alloy melt for AlSi12Fe die-casting is prepared. The "melt" mentioned in this embodiment refers to an aluminum alloy melt for AlSi12Fe die-casting.

[0020] Reference Figure 1 The preparation method of the aluminum alloy melt for die casting shown in the figure comprises the following steps: Charge configuration step S1: According to the quality requirements of aluminum alloy products, aluminum alloy ingots with the grade of AlSi12Fe and recycled materials with the corresponding grade of AlSi12Fe are configured into charge in proportion.

[0021] The above-mentioned recycled materials can be divided into three levels according to their quality. Level 1 recycled materials: clean castings that are not scrapped due to impurity content exceeding the standard can be directly used for batching without remelting, and their usage generally does not exceed 80% of the amount of recycled materials. Level 2 recycled materials: gates, material handles, etc. of die castings, the usage generally does not exceed 60% of the amount of recycled materials. Level 3 recycled materials: waste materials such as oily castings, slag bags, flash, etc., need to be remelted and analyzed for composition before being used for batching, and their usage generally does not exceed 30% of the amount of recycled materials. Using recycled materials means recycling the waste and waste materials generated during the refining process, which is beneficial to environmental protection and saves production costs.

[0022] Aluminum alloy melt preparation step S2: add a charge having a volume of 85% of the volume of the graphite crucible furnace into a crucible furnace at 900±50°C, heat the charge until it melts, and obtain an aluminum alloy melt. Since cracks often form on the upper end of the graphite crucible furnace and residues are attached, refining the charge according to 85% of the furnace volume as one furnace can prevent the melt from being contaminated by the residues.

[0023] Before putting the charge into the graphite crucible furnace, it is necessary to remove oil, rust, sand, and inlays according to the actual situation. In particular, the charge needs to be preheated to remove the moisture on the surface of the charge, so as to prevent the wet charge from exploding due to a sudden temperature rise after entering the furnace. The charge is put into the graphite crucible furnace once or twice to prevent the increase of the content of oxide inclusions and gases in the melt.

[0024] The first sampling and testing step S20: After the temperature of the aluminum alloy reaches 730°C and the aluminum alloy is completely melted, slag sampling can be performed. That is, the slag on the surface of the aluminum alloy melt is scraped off, and the aluminum alloy melt sample to be inspected is taken out from the graphite crucible furnace, and the aluminum alloy melt sample is analyzed for alloy elements using a spectrometer to determine whether the element composition of the aluminum alloy melt is qualified (S20a). If it is unqualified, the corresponding furnace charge should be added in time to adjust until the composition of the aluminum alloy melt is verified to be qualified.

[0025] The tool used for slag removal is a 5mm thick stainless steel slag spoon. Since it will not rust, it can prevent rust from contaminating the aluminum alloy melt.

[0026] Figure 2The sampling result of the first sampling detection step S20 is shown, that is, the AlSi12Fe aluminum alloy melt that has just been melted and has not been processed in subsequent steps. It can be seen that many large bubbles 1 with irregular shapes are formed in the melt due to the high hydrogen content, and obviously uneven slag can be seen from the inside of the bubbles, indicating that the hydrogen and slag contents in the melt are relatively high.

[0027] Transfer step S30: Heat the aluminum alloy melt to 760-800°C and pour it into the preheated transfer bag, then start the refining agent degassing step S3. If the first sampling test step S20 is qualified, continue to heat and increase the temperature of the aluminum alloy melt, which can save refining time and energy for heating. Preheating the transfer bag to 770-830°C can avoid excessive heat loss during the process of pouring the melt into the transfer bag.

[0028] The refining agent degassing step S3 includes the following sub-steps: The first stage graphite rotor adjustment sub-step S31: After the graphite rotor is preheated, it is inserted into the transfer bag and rotated at a speed of 400 rpm to stir the aluminum alloy melt into a vortex shape.

[0029] The first ventilation sub-step S32: while the graphite rotor is rotating, an inert gas is introduced into the aluminum alloy melt, wherein nitrogen with a purity of 99.99% is selected, the flow rate is 35L / min, and the pressure is 0.2Mpa. These inert gases can protect the graphite rotor, avoid internal blockage of the rotor due to lack of airflow, and avoid such failure affecting the next step, and also avoid excessive flow or pressure in the transfer bag, which may cause the melt to splash and injure people.

[0030] Adding slag refining agent sub-step S33: adding slag refining agent to the aluminum alloy melt, the amount of which is 1-2% of the weight of the melt. The slag refining agent can be sunk to the bottom by the adsorption effect of the vortex formed in the first stage graphite rotor adjustment sub-step S31.

[0031] The above-mentioned slag-refining agent is a mixture of a refining agent and a slag-removing agent, the refining agent is manganese chloride or zinc chloride, the slag-removing agent is a mixture of sodium chloride, calcium chloride, cryolite, and sodium fluorosilicate, and the refining agent and the slag-removing agent are mixed in a weight ratio of 1:1.5. After actual testing, the slag-refining agent with the above-mentioned components has the best effect.

[0032] The first refining sub-step S34: after adding the slag refining agent, the aluminum alloy is refined at a temperature of 720-780°C for 8 minutes. In this process, harmful substances such as oxide film and inclusions in the aluminum alloy melt will separate from the melt and float to the surface of the melt.

[0033] The above refining agent degassing step S3 can be completed using an existing degassing refiner, such as the utility model patent with application number 201922455622.4, entitled Aluminum Melt Refining Degassing Machine, which will not be described in detail here. This embodiment uses a fixed degassing refiner with a PLC system and a frequency converter, which can accurately control the dosage and the speed of the graphite rotor.

[0034] Figure 3 The results of the dissection of the AlSi12Fe aluminum alloy melt after the refining agent degassing step S3 for 8 minutes are shown. It can be seen that after 8 minutes of refining, the bubble 2 in the figure is smaller than that in the Figure 2 The bubbles 1 in the sample are obviously smaller and more regular, indicating that the contents of slag and hydrogen in the melt are significantly reduced, and the slag refining agent has a significant effect.

[0035] After the refining agent degassing step S3, the inert gas degassing step S4 is immediately performed.

[0036] The inert gas degassing step S4 comprises the following sub-steps: The second stage graphite rotor adjustment sub-step S41: increasing the graphite rotor speed to 675 rpm to provide more rotational energy for the melt and form turbulence.

[0037] Second stage ventilation sub-step S42: while adjusting the rotation speed of the graphite rotor, increase the flow rate of the inert gas to 2500 L / min and the gas pressure to 0.3 MPa.

[0038] Inserting slag blocking plate sub-step S41: While adjusting the rotation speed of the graphite rotor, the slag blocking plate is controlled to fall down to a position 10 cm deep on the surface of the filtrate to block the slag aside.

[0039] The second refining sub-step S42: refining at a temperature of 720-780°C for 15 minutes. In this process, the inert gas is broken into small bubbles by the high-energy aluminum alloy melt, and the slag-like impurities such as solids such as alumina and residues of slag refining agents are carried upwards during the floating of the small bubbles. These impurities are intercepted by the slag baffle on one side of the top of the aluminum alloy melt and will not be mixed into the aluminum alloy melt.

[0040] The inert gas degassing step S4 can be directly pre-set in the program of the degassing refiner so that it can be completed automatically. It only needs to pre-set the graphite rotor speed, ventilation volume, and slag plate falling time. It is easy to operate and has a high degree of automation. It does not require the transfer of the melt or static refining, has low heat loss, and high refining efficiency.

[0041] After the inert gas degassing step S4, the second sampling and testing step S50 is performed.

[0042] The second sampling and testing step S50: remove the scum on the surface of the aluminum alloy melt, take samples to check whether the gas content in the aluminum alloy melt is qualified. If qualified, the die casting preparation step S5 can be carried out, that is, the aluminum alloy melt with qualified gas content is transferred from the transfer bag to the insulation furnace, the temperature of the aluminum alloy melt is adjusted to the range required for die casting, and the temperature is kept, waiting for die casting. If it is unqualified, the inert gas degassing step S4 is carried out again for a certain period of refining.

[0043] The gas content detection is carried out on a vacuum hydrogen tester. Through the action of the vacuum pump, the vacuum degree in the detection chamber reaches 75%-80%, which is enough to detect the gas content in the prepared melt in real time. In addition, before slagging, the slag on the rotor and shaft must be cleaned to prevent the slag from contaminating the melt.

[0044] Figure 5 The dissection results of the AlSi12Fe aluminum alloy melt sampled after the inert gas degassing step S4 are shown. It can be seen that after continuing to smelt for 15 minutes, the hydrogen content and slag content in the aluminum alloy melt are significantly reduced, and only a very small number of uneven small holes 3 are present, which meets the quality requirements of the aluminum alloy melt for die casting, effectively reduces the formation of pores, looseness, inclusions and other defects in the aluminum alloy die castings, and can ensure that the physical properties, mechanical properties and performance of the aluminum alloy die castings are met.

[0045] Embodiment 2 In this embodiment, ADC12 aluminum alloy melt for die casting is prepared. The "melt" mentioned in this embodiment is ADC12 aluminum alloy melt for die casting.

[0046] In addition to the chemical composition of the charge, melt, aluminum ingot, and recycled material being different from that of the first embodiment, the present embodiment also has the following parameters different from those of the first embodiment: Refining agent degassing step S3: the inert gas flow rate in the first ventilation sub-step S32 is 25 L / min; the refining time of the first refining sub-step S34 is 7 minutes.

[0047] Inert gas degassing step S4: increase the graphite rotor speed to 600 rpm; second stage ventilation sub-step S42: increase the flow rate of the introduced inert gas to 2000 L / min.

[0048] Figure 5 The results of sampling and dissection of the ADC12 melt that has not undergone the refining agent degassing step S3 and the inert gas degassing step S4 are shown. It can be seen that many large bubbles 4 with irregular shapes are formed in the melt due to the high hydrogen content, and obviously uneven slag-like materials can be seen from the inside of the bubbles, indicating that the hydrogen and slag contents in the melt are relatively high.

[0049] Figure 6The dissection results of the ADC12 melt sample after the refining agent degassing step S3 and without the inert gas degassing step S4 are shown. It can be seen that after 7 minutes of refining, the bubble 5 in the figure is smaller than that in the Figure 2 The bubbles 1 in the melt become significantly smaller and more regular, and the interiors of most bubbles become smooth, indicating that the contents of slag and hydrogen in the melt are significantly reduced.

[0050] Figure 7 The dissection results of ADC12 melt sampling after the refining agent degassing step S3 and the inert gas degassing step S4 are shown. It can be seen that after continuing to smelt for 10 minutes, the hydrogen content and slag content in the aluminum alloy melt are significantly reduced, and there are only a very small number of uneven small holes 6, which meets the quality requirements of aluminum alloy melt for die casting, effectively reduces the formation of pores, looseness, inclusions and other defects in aluminum alloy die castings, and can ensure that the physical properties, mechanical properties and performance of aluminum alloy die castings are met.

[0051] Figure 8 The state of the degassing refiner during the refining agent degassing step S3 is shown. Fig. 9 The state of the degassing refiner during the inert gas degassing step S4 is shown below in conjunction with the attached Figure 8 , 9 The beneficial effects of the present invention are described.

[0052] like Figure 8 As shown, the graphite rotor 21 is inserted into the transfer bag 20 and rotates in the direction of arrow a, so that the aluminum alloy melt in the transfer bag forms a vortex (in Figure 8 In the graphite rotor 21, a pipe 24 for conveying inert gas is provided. The inert gas is ejected from the bottom of the graphite rotor 21 in the direction of the arrow b in the figure. The bubbles formed by these inert gases will not affect the formation of the vortex, and can push the slag refining agent away, playing the role of dispersing the slag refining agent, so that the slag refining agent flows faster with the vortex, which can promote the slag refining agent to be evenly mixed with the aluminum alloy melt, increase the contact area between the two, and improve the degassing and deslagging efficiency and deslagging effect of the refining agent.

[0053] That is, the gas (aluminum chloride) generated by the chemical reaction between the slag refining agent and the aluminum alloy melt is mainly concentrated in the contact part between the slag refining agent and the aluminum alloy melt, and it is difficult for the refining slag refining agent to be quickly and evenly dispersed in the aluminum alloy melt. During the refining process, after the above-mentioned quantitative inert gas is introduced into the aluminum alloy melt, under the stirring of the rotating graphite rotor, the inert gas is dispersed into the aluminum alloy melt in the form of bubbles, which drives the slag refining agent to move, so that the slag refining agent can be more quickly and evenly dispersed in the aluminum alloy melt rotating in a vortex shape, and has better contact with the aluminum alloy melt, which promotes the uniform generation of aluminum chloride gas in the aluminum alloy, so as to effectively optimize the refining effect and improve the refining efficiency.

[0054] like Fig. 9 As shown, in the inert gas degassing step S4, the rotation speed of the graphite rotor 21 increases, which adds energy to the aluminum alloy melt and forms a turbulent flow (with Figure 8 compared to, Fig. 9 The "V"-shaped vortex in the center of the upper surface of the middle melt becomes significantly smaller), the slag baffle plate 23 falls and penetrates into the aluminum alloy melt, and a large amount of inert gas (2000-2500 L / min) introduced along the arrow d is broken into small bubbles by the high-energy aluminum alloy melt and dispersed in the aluminum alloy melt, fully contacting with the aluminum alloy melt, and in the process of small bubbles floating up, solids such as alumina and slag-like impurities such as residues of slag refining agent are brought upward.

[0055] After the refining agent degassing step S3, the speed of the graphite rotor, the flow rate and air pressure of the inert gas are directly increased, and the process is simple and convenient. Since no more medicine is added during the inert gas degassing step S4, it is not necessary to keep the aluminum alloy melt in a state with a vortex. The rotation speed is increased under the premise of safe production, which can make the aluminum alloy melt form turbulence, which is more conducive to the small bubbles formed by the inert gas. There is no need to transport the aluminum alloy melt between the refining agent degassing step S3 and the inert gas degassing step S4, which avoids the aluminum alloy melt from contacting with air to dissolve hydrogen and impurities such as mixed aluminum oxide again when the aluminum alloy melt is transported to the degassing equipment, further improving the effect of degassing and impurity removal, and the efficiency of degassing and slag removal is high.

[0056] It is also worth noting that the order of the refining agent degassing step S3 and the inert gas degassing step S4 cannot be changed. On the one hand, the inert gas degassing step S4 can fully remove the large particles of slag and other impurities separated from the aluminum alloy melt in the refining agent degassing step S3 and the remaining slag refining agent residue, which saves more time, is conducive to improving production efficiency, and is also conducive to controlling the amount of medicine; on the other hand, placing the inert gas degassing step S4 later is more conducive to controlling the duration of the entire refining and degassing process according to product quality requirements. The staff can optimize the refining time according to product requirements, thereby improving the overall production efficiency: That is, the inert gas degassing step S4 is a highly controllable step whose duration can be designed according to product requirements. In actual production, the precision requirements for aluminum alloy materials used in die-cast parts of different products are different. For example, parts of indoor communication products will not be exposed to rain, so the requirements for the impermeability of aluminum alloy materials are not high, and a small amount of hydrogen can be allowed in the material. The inert gas degassing step S4 can be set for a shorter time (10 minutes) to further ensure production efficiency; while automotive parts commonly used outdoors have extremely high requirements for the impermeability of aluminum alloy materials and very strict quality requirements for aluminum alloy materials. The time of the inert gas degassing step S4 needs to be set for a longer time (25 minutes) to ensure the refining effect and product quality.

[0057] It should be noted that the above embodiments illustrate rather than limit the present invention, and those skilled in the art may design alternative embodiments without departing from the scope of the appended claims. For example, the inert gas uses 99.99% argon.

[0058] For ease of understanding, the principles involved in the present invention are further explained below: The refining quality of aluminum alloy materials, such as hydrogen content, oxide layer, inclusions and other defects, has always been a long-standing problem that plagues the die-casting industry. Aluminum has a great affinity for oxygen. When aluminum and its alloy liquid come into contact with air, it is easy to form an oxide film (Al2O3). Although the oxide film on the surface of the melt has a protective effect, after being destroyed, its density is very close to that of the melt, and it is suspended in the melt. If it is not removed, it will enter the casting with the melt.

[0059] Aluminum and its alloy liquids can easily absorb hydrogen from the air, alloy ingots and moisture on the surface of tools. The solubility of hydrogen in the solid state is very low. Therefore, if the die casting is not degassed, hydrogen will precipitate while the casting solidifies, causing defects such as pores and shrinkage holes in the casting. Common inclusions in aluminum alloy melts are Al2O3, SiO2, MgO, etc., which will cause the metal liquid to be impure, affect the fluidity of the melt, and aggregate in the die casting to produce bubbles, affecting the shrinkage degree of the casting.

[0060] The reaction between the aluminum alloy liquid and the iron crucible lining produces slag. The black and gray particles visible on the cutting surface of the casting are slag. Slag includes non-metallic oxides, metal compounds, composite slag and segregation slag. The aluminum alloy liquid has a certain dissolution with the crucible, spoon, tools and molds, resulting in an increase in iron content. The iron content in the return material is much greater than the specified value. On the other hand, since the die casting will inevitably produce material handles, runners, slag bags, scrap parts, etc., which are collectively referred to as return materials in the die casting industry, in order to save costs, return materials will be added in proportion during the refining process of aluminum alloys, which will aggravate the presence of harmful substances such as hydrogen, oxide film, inclusions, etc. in the melt, and defects such as pores, looseness, inclusions, etc. are easily formed in aluminum alloy die castings, which directly affect the physical properties, mechanical properties and performance of aluminum alloy die castings. Therefore, these harmful substances must be removed before pouring.

[0061] The refining agent with the active ingredient of chloride salt, the specific refining principle is: the chloride salt reacts with aluminum to generate volatile aluminum chloride (AlCl3), and a mechanical tumbling effect occurs during the volatilization process, bringing out gas and impurities. For example, the chemical reaction of zinc chloride and manganese chloride:

[0062] 3ZnCl2+2Al → 3Zn+2AlCl3↑, 3MnCl2+2Al → 3Mn+2AlCl3↑, aluminum chloride (AlCl3) is in a vapor state (boiling point is 183℃), and it also participates in the hydrogen removal process.

[0063] At present, the method of removing hydrogen from aluminum alloy melt is mainly based on the bubble floating theory, that is, a large number of bubbles are blown into the aluminum alloy melt, and the large inert gas bubbles are broken into very small bubbles by a high-speed rotating rotor, and they are diffused in the entire molten metal. By reducing the bubble diameter, the surface of the inert gas is greatly increased, so that more inert gas surfaces are in contact with hydrogen and impurities in the molten metal, and hydrogen or impurities are removed from the aluminum liquid as the bubbles rise. The partial pressure difference of hydrogen in the aluminum melt and the bubbles is used to make the hydrogen in the aluminum melt continuously diffuse into the bubbles, and escape as the bubbles float to the surface of the melt, thereby achieving the purpose of removing hydrogen. There are two main theoretical models proposed to explain the principle of degassing. The macroscopic model believes that the removal of each impurity is essentially similar. The microscopic model, that is, the above theory, due to the high vapor pressure of hydrogen, the dissolved hydrogen diffuses into the gas in the injected aluminum alloy liquid. Theoretically, after an inclusion with a diameter of 10 microns comes into contact with a bubble, it is adsorbed on the bubble and floats to the surface of the liquid.

[0064] In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Claims

1. A method for preparing an aluminum alloy melt for die casting, characterized in that: include: Charge configuration step (S1): According to the requirements of aluminum alloy products, aluminum alloy ingots and recycled materials are configured into charge in proportion. Melt preparation step (S2): placing the charge into a graphite crucible furnace, heating and melting the charge, and performing a slag removal operation to remove slag on the surface to obtain an aluminum alloy melt; Refining agent degassing step (S3): pouring the aluminum alloy melt at a temperature of 760-800° C. from the graphite crucible furnace into a transfer bag, rotating the rotor at a speed of 400-600 rpm, introducing an inert gas into the aluminum alloy melt at a flow rate of 25-35 L / min and a gas pressure of 0.2 MPa, stirring the aluminum alloy melt into a vortex, adding a refining agent and / or a slag remover into the aluminum alloy melt in an amount of 1-2% of the weight of the melt, using the adsorption effect of the vortex to sink the refining agent and / or the slag remover to the bottom, and refining at a temperature of 720-780° C. for 7-8 minutes; Inert gas degassing step (S4): dropping a slag baffle into the transfer bag to allow the slag baffle to penetrate into the aluminum alloy melt, adjusting the rotor speed, the flow rate and pressure of the inert gas, adjusting the rotor speed from 400-600 / min to 600-675 rpm, adjusting the flow rate of the inert gas from 25-35 L / min to 2000-2500 L / min, and adjusting the gas pressure from 0.2 Mpa to 0.3 Mpa, and continuing refining for 10-15 minutes. Die casting preparation step (S5): After slagging, the aluminum alloy melt that has been refined and degassed is transferred from the transfer bag to a holding furnace, and the temperature of the aluminum alloy melt is adjusted to a range required for die casting.

2. The preparation method according to claim 1, characterized in that: In the refining agent degassing step (S3), a mixture of a refining agent and / or a slag-breaking agent is added. The refining agent is manganese chloride or zinc chloride, and the slag-breaking agent is a mixture of sodium chloride, calcium chloride, cryolite, and sodium fluorosilicate. The refining agent and the slag-breaking agent are mixed in a weight ratio of 1:1.

5.

3. The preparation method according to claim 1, characterized in that: The charge includes fresh alloy aluminum ingots and recycled charge. In the melt preparation step (S2), before the charge is put into the graphite crucible furnace, the charge is degreased, rusted, silted, and inlaid, and the charge is preheated. The charge is put into the graphite crucible furnace once or twice, and the furnace temperature is set at 900±50°C. When the temperature reaches 730°C, slag is removed to obtain an aluminum alloy melt.

4. The preparation method according to claim 1, characterized in that: In the melt preparation step (S2), after slagging, the aluminum alloy melt is sampled for spectral sample chemical composition detection to obtain the aluminum alloy melt for refining.

5. The preparation method according to claim 4, characterized in that: In the refining agent degassing step (S3) and the inert gas degassing step (S4), the inert gas introduced is nitrogen or argon with a purity of 99.99%.

6. The preparation method according to claim 1, characterized in that: In the die casting preparation step (S5), after slag removal, sampling is performed to check whether the gas content in the aluminum alloy melt is qualified. If it is unqualified, the inert gas degassing step (S4) is performed again.

7. The preparation method according to claim 3, characterized in that: The recycled materials include primary recycled materials, secondary recycled materials and tertiary recycled materials. The first-grade recycled materials refer to clean castings that are not scrapped due to impurity content exceeding the standard, and can be directly used for batching without remelting, not exceeding 80% of the total weight of the recycled materials. The secondary recycled materials refer to the gate and handle of the die casting, which shall not exceed 80% of the total weight of the recycled materials. The third-level recycled materials refer to waste materials containing oily castings, slag bags, flash, etc., which need to be remelted and analyzed for composition before being used for batching, and shall not exceed 30% of the total weight of the recycled materials.

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